Kallikrein 7 is a S1 serine protease of the kallikrein gene family displaying a chymotrypsin like activity. Human kallikrein 7 (hK7, KLK7 or stratum corneum chymotryptic enzyme (SCCE), Swissprot P49862) plays an important role in skin physiology (1, 2, 3). It is mainly expressed in the skin and has been reported to play an important role in skin physiology. hK7 is involved in the degradation of the intercellular cohesive structures in cornified squamous epithelia in the process of desquamation. The desquamation process is well regulated and delicately balanced with the de novo production of corneocytes to maintain a constant thickness of the stratum corneum, the outermost layer of the skin critically involved in skin barrier function. In this regard, hK7 is reported to be able to cleave the corneodesmosomal proteins corneodesmosin and desmocollin 1 (4, 5, 6). The degradation of both corneodesmosomes is required for desquamation. In addition, very recently it has been shown that the two lipid processing enzymes 3-glucocerebrosidase and acidic sphingomyelinase can be degraded by hK7 (7). Both lipid processing enzymes are co-secreted with their substrates glucosylceramides and sphingomyelin and process these polar lipid precursors into their more non-polar products e.g. ceramides, which are subsequently incorporated into the extracellular lamellar membranes. The lamellar membrane architecture is critical for a functional skin barrier. Finally, hK7 has been shown to activate Interleukin-1β (IL-1β) precursor to its active form in vitro (8). Since keratinocytes express IL-1β but not the active form of the specific IL-1β converting enzyme (ICE or caspase 1), it is proposed that IL-1β activation in human epidermis occurs via another protease, a potential candidate being hK7.
Recent studies link an increased activity of hK7 to inflammatory skin diseases like atopic dermatitis, psoriasis or Netherton's syndrome. This might lead to an uncontrolled degradation of corneodesmosomes resulting in a miss-regulated desquamation, an enhanced degradation of lipid processing enzymes resulting in a disturbed lamellar membrane architecture or an uncontrolled activation of the proinflammatory cytokine IL-1β. The net result would be an impaired skin barrier function and inflammation (see also WO-A-2004/108139).
Due to the fact that the hK7 activity is controlled at several levels, various factors might be responsible for an increased hK7 activity in inflammatory skin diseases. Firstly, the amount of protease being expressed might be influenced by genetic factors. Such a genetic link, a polymorphism in the 3′-UTR in the hK7 gene, was recently described (9). The authors hypothesise that the described 4 base pair insertion in the 3′-UTR of the kallikrein 7 gene stabilizes the hK7 mRNA and results in an overexpression of hK7. Secondly, since hK7 is secreted via lamellar bodies to the stratum corneum extracellular space as zymogen and it is not able to autoactivate, it needs to be activated by another protease e.g. hK5 (5). Uncontrolled activity of such an activating enzyme might result in an overactivation of hK7. Thirdly, activated hK7 can be inhibited by natural inhibitors like LEKTI, ALP or elafin (10, 11). The decreased expression or the lack of such inhibitors might result in an enhanced activity of hK7. Recently it was found, that mutations in the spink5 gene, coding for LEKTI, are causative for Netherton's syndrome (12) and a single point mutation in the gene is linked to atopic dermatitis (13, 14). Finally, another level of controlling the activity of hK7 is the pH. hK7 has a neutral to slightly alkaline pH optimum (2) and there is a pH gradient from neutral to acidic from the innermost to the outermost layers in the skin. Environmental factors like soap might result in a pH increase in the outermost layers of the stratum corneum towards the pH optimum of hK7 thereby increasing the hK7 activity.
The hypothesis that an increased activity of hK7 is linked to skin diseases with an impaired skin barrier including inflammatory and hyperpoliferative skin diseases is supported by the following studies: Firstly, Netherton's syndrome patients show a phenotype dependent increase in serine protease activity, a decrease in corneodesmosomes, a decrease in the lipid processing enzymes β-glucocerebrosidase and acidic sphingomyelinase, and an impaired barrier function (15, 16). Secondly, a transgenic mice overexpressing human kallikrein 7 shows a skin phenotype similar to that found in patients with atopic dermatitis (17, 18, 19). Thirdly, in the skin of atopic dermatitis and psoriasis patients elevated levels of hK7 were described (17, 20). Furthermore, increased activity of K7 and thus epithelial barrier dysfunction may also play an important role in the pathology of other epithelial diseases such as inflammatory bowel disease and Crohn's disease.
Therefore, hK7 is considered to be a potential target for the treatment of diseases involved with epithelial dysfunction such as inflammatory and/or hyperpoliferative and pruritic skin diseases like atopic dermatitis, psoriasis, Netherton's syndrome or other pruritic dermatoses such as prurigo nodularis, unspecified itch of the elderly as well as other diseases with epithelial barrier dysfunction such as inflammatory bowel disease and Crohn's disease and there is a need for specific modulators (agonists or inhibitors) thereof.
Treatment can be by local or systemic application such a creams, ointments and suppositories
or by oral or sc or iv application, respectively.
Chondromyces is a genus in the family Polyangiaceae, which belongs to the order Myxococcales within the Delta-proteobacteria. Bacteria of the order Myxococcales, also called myxobacteria, are gram-negative rod-shaped bacteria with two characteristics distinguishing them from most other bacteria. They swarm on solid surfaces using an active gliding mechanism and aggregate to form fruiting bodies upon starvation (Kaiser (2003)). The present inventors have identified cyclic depsipeptide produced by Chondromyces that are able to specifically modulate kallikrein 7.